The cheaps ones, usually chocolate chip starfish. The cheapest method is to stock up a few of them in a sump/QT and chop off a leg of each star until the first regrows its leg, 'rotation method'. They won't touch brittles or serpents, and I've yet to actually witness predation on urchins like some claim.
Bumblebees there's this very little to no evidence of actually eating starfish, to the point its safe to say they don't eat them anymore than crabs probably.
Even if there was and they did they wouldn't target them exclusively, it'd just be something they'd occasionally pick on. You're probably going to end up buying several of them to no noticeable effect, but if you do let us know how that goes and try recording one eating a star.